Downhole separation and injection of produced water in naturally flowing or gas-lifted hydrocarbon wells

ABSTRACT

A method and system for the downhole separation and injection of a predominately water component of the mixture produced from a naturally flowing or gas-lifted hydrocarbon well. The produced mixture is delivered to a separator located in the wellbore above an injection formation, the separator comprising a gas-liquid separator and an oil-water separator. The produced mixture is admitted to a gas-liquid separator to separate the free gas from the produced mixture. The gas-depleted produced mixture is then admitted to an oil-water separator where the produced mixture is separated into a predominately water component and a predominately hydrocarbon component. The separated gas and the predominately hydrocarbon component are delivered to the surface, separately or commingled. The predominately water is injected in the injection formation accessible through the same wellbore, and located below the separator. The predominately water component is separated at a sufficiently elevated location with respect to the injection formation to permit the predominately water component to be delivered to the injection formation under the force of gravity. This invention achieves downhole water separation and injection without having to install downhole pumps to re-inject the water contained in the produced mixture.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is generally directed to a method and system forthe downhole separation and injection of water contained in producedmixtures from a production zone of a hydrocarbon well.

2. Background

In many hydrocarbon wells, there is a high percentage of water (referredto as water cut) in the produced fluid mixture. In typical practice, theproduced fluid is lifted to the surface and the water is separated fromhydrocarbon at the surface. Surface separated water is subsequentlytreated and disposed of on the surface or re-injected into asubterranean formation for disposal or as part of an enhanced reservoirrecovery program. This process is not always entirely satisfactorybecause of the energy needed to lift the water to surface, and costsinvolved in separation of the water and hydrocarbon fluid, andre-injection of the water.

In many cases, it might be more economical to separate the waterdownhole in the same wellbore and re-inject it into a suitable zoneaccessible through the same wellbore. Examples of methods for thedownhole separation and re-injection of water contained in fluidsproduced from hydrocarbon wells have been described in the patentliterature: WO86/03143, U.S. Pat. Nos. 4,805,697, 5,296,153, 5,456,837,5,711,374, and 5,730,871. These approaches describe various means toachieve downhole separation of oil and water components of producedfluids with subsequent lifting of separated oil to the wellhead. Theseapproaches rely on downhole pumps to re-inject the water component intoa suitable zone, and to bring the oil to surface.

In order to drive a downhole pump, some form of power, be it mechanical,electrical or hydraulic, must be transmitted from surface to the pump.Hydrocarbon wells are often located in places where providing for powerfor such functions is not convenient.

In offshore wells, gas-lift systems are often preferred due to thesimplicity and reliability of their associated downhole components. Insuch techniques, compressed gas is commingled downhole with the producedfluids, thereby reducing the density of the produced fluids until theweight of the column of the gasified fluids becomes less than thepressure exerted on the body of fluids in the well, and flow of producedfluids to the surface is facilitated. Examples of the gas-lift techniqueare described in U.S. Pat. Nos. 5,217,067, 4,251,191, and 3,718,407.

U.S. Pat. No. 5,857,519 describes an approach for the downhole disposalof the water component of produced fluids while using gas lifttechniques to lift the oil component to the surface. The oil and watercomponents are separated downhole by gravity in an annular space locatedbetween a production tubing and the wellbore casing. Pressurized gas isused to drive a downhole pump that re-injects downhole-separated water,and exhaust gas from the downhole pump is used to assist in the liftingof oil to the wellhead.

Using present technology, downhole separation and disposal of water in awellbore require downhole pumps. The present technology is therefore,inherently plagued with two main problems: 1) complex completionsassociated with providing power from surface to drive downhole pumps,and 2) poor reliability of the downhole pumps.

SUMMARY OF THE INVENTION

What is required is a method and system for the downhole separation andinjection of water contained in produced mixtures from hydrocarbon wellsthat does not require downhole pumps. Accordingly, the present inventionconcerns a method and system for separating and injecting downhole, thewater contained in the produced mixture of a hydrocarbon well whilelifting hydrocarbon contained in the produced mixture to surface withoutthe use of a downhole pump.

According to an aspect of the present invention, there is provided amethod for the downhole separation and injection of a predominatelywater component of a production fluid comprising at least some water andat least some oil from a production zone of a hydrocarbon wellcomprising the steps of separating downhole, at a position elevated withrespect to an injection formation, the production fluid into apredominately water component and a predominately hydrocarbon componentand delivering the predominately water component to the downholeinjection formation, wherein the separating step is conducted at asufficiently elevated location with respect to the injection formationto permit the predominately water component to be delivered to thedownhole injection formation under the force of gravity. In accordancewith a preferred embodiment of the invention, the method furthercomprises injecting gas into the production fluid to deliver theproduction fluid to the elevated position in the well. In anotherpreferred embodiment, the injected gas is delivered downhole through agas-lift string that extends from the head of the well.

In accordance with yet another preferred embodiment, the productionfluid is delivered to the elevated position by way of a conduit thatextends from the production formation to the elevated position. Inaccordance with yet another preferred embodiment, the production fluidis delivered to the elevated position by way of an annular space withinthe well.

In a preferred embodiment of the invention, the percentage of water inthe production fluid is at least 20%.

In accordance with yet another preferred embodiment of the invention,the production fluid contains gas. In accordance with yet anotherpreferred embodiment, gas is separated from the production fluid andthis step optionally precedes the step of separating the productionfluid into a predominately water component and a predominatelyhydrocarbon component. In yet another preferred embodiment of theinvention, the separated gas is delivered to the surface.

In accordance with yet another preferred embodiment of the invention,the mostly hydrocarbon component is transported to the surface. Inaccordance with yet another preferred embodiment of the invention, theseparated gas and the predominately hydrocarbon component are combinedand delivered to the surface. In a preferred embodiment of the presentinvention, a mixing device is used to combine gas and the mostlyhydrocarbon component of the production fluid.

In accordance with another aspect of the invention, there is provided asystem for the downhole separation and injection of a predominatelywater component of a production fluid comprising at least some water andat least some oil from the production formation of a hydrocarbon well.The system comprises an oil-water separator located downhole at aposition elevated with respect to an injection formation, a firstpassage to provide fluid communication between the production formationand an inlet of the separator, and a second passage to provide fluidcommunication between the water outlet of the separator and a downholeinjection formation. The separator is located at a sufficiently elevatedlocation with respect to the injection formation to permit the mostlywater component emerging from the water outlet to be delivered to thedownhole injection formation under the force of gravity.

In a preferred embodiment, the oil-water separator comprises at leastone cyclone.

In another preferred embodiment of the present invention, the systemfurther comprises means for injecting gas into the production fluid inorder to deliver the production fluid to the separator such as a conduitextending between the head of the well and the production formation.

In yet another preferred embodiment, the system includes a gas-liquidseparator located at an elevation at least as high as the oil-waterseparator and having a gas-liquid inlet in fluid communication with theproduction fluid for receiving the production fluid as well as an outletfor passage of liquid from the gas-liquid separator to the oil-waterseparator. In a preferred embodiment, the gas-liquid separator comprisesat least one cyclone. In another preferred embodiment, the gas-liquidseparator comprises at least one auger. In yet another preferredembodiment, the gas-liquid separator comprises a combination of at leastone cyclone and at least one auger connected in series or in parallel.In yet another preferred embodiment, the cyclone incorporates a swirlgenerator.

In yet another preferred embodiment, the system includes a third passagethat extends between the oil outlet of the oil-water separator and thehead of the well.

In yet another preferred embodiment, the system includes means forinjecting gas into the third passage to promote flow of the mostlyhydrocarbon component of the production fluid from the oil outlet to thehead of the well. Means can include a conduit for providing fluidcommunication between a gas outlet of the gas-liquid separator and thethird passage.

In accordance with yet another aspect of the invention, there isprovided a method of completing a well for production of hydrocarbonfrom an underground formation comprising installing an oil-waterseparator downhole at a position elevated with respect to the injectionformation, providing a first passage for fluid communication between theproduction formation and an inlet of the separator, providing a secondpassage that is isolated from the first passage for fluid communicationbetween the water outlet of the separator and the injection formation,and locating the separator at a sufficiently elevated location withrespect to the injection formation to permit fluid emerging from thewater outlet to be delivered to the downhole injection formation underthe force of gravity.

In a preferred embodiment of the present invention, providing anoil-water separator comprises installing at least one cyclone.

In another preferred embodiment of the present invention, the methodfurther comprises providing means for injecting gas into the productionfluid in order to deliver the production fluid to the separator. In apreferred embodiment, a conduit extending between the head of the welland the production formation is provided to provide means for injectinggas.

In yet another preferred embodiment, the method further comprisesproviding a gas-liquid separator located at an elevation at least ashigh as the oil-water separator and having a gas-liquid inlet in fluidcommunication with the production fluid for receiving the productionfluid as well as an outlet for passage of liquid from the gas-liquidseparator to the oil-water separator. In a preferred embodiment, thegas-liquid separator comprises a cyclone. In another preferredembodiment, the gas-liquid separator comprises an auger.

In yet another preferred embodiment, the method further comprisesproviding a third passage that extends between the oil outlet of theoil-water separator and the head of the well.

In yet another preferred embodiment, the method further comprisesproviding means for injecting gas into the third passage to promote flowof the mostly hydrocarbon component of the production fluid from the oiloutlet to the head of the well. Means include a conduit for providingfluid communication between a gas outlet of the gas-liquid separator andthe third passage.

With the present method and system, there does not need to be a downholepump to inject the downhole-separated water component of producedfluids. The separator is located in a position in the wellbore so as toproduce the predominately water component at a sufficient pressure sothat it may be injected downhole without the use of a pump. Thisvariable position of the separator can also lead to a reduction ingas-lift requirements. The lower the injection pressure needed to injectthe water, the lower the location of the separator which in turn resultsin reduced artificial lift requirements. Also, with the present system,the produced mixture can be lifted to the separator in either adedicated tube or annular space. This arrangement leads to a variabletubing configuration for optimizing flow of fluids in the wellbore.Potential benefits include increased production rates in wells currentlyproduction limited due to existing tubular and surface facilities,reduction of water handling (both processing and disposal) at thesurface, elimination of surface infrastructure for powering downholepumps, reduced gas-lift usage, reductions in the cost of running highwater cut hydrocarbon wells, improved system reliability andenvironmental benefits from reduced discharge of produced water. Aswell, gas separated from produced fluids downhole can be commingled andbrought to surface with downhole separated oil to reduce tubingrequirements in the well.

Other and further advantages and features of this invention will beapparent to those skilled in the art from the following detaileddescription thereof, taken in conjunction with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features of the present invention are more fully setforth in the following description of illustrative embodiments of theinvention. The description is presented with reference to theaccompanying drawing in which:

FIG. 1 is a schematic representation of an embodiment of the presentinvention in which the total produced mixture is delivered to agas-liquid separator by way of a conduit extending from an undergroundproduction zone to the separator;

FIG. 2 is a schematic diagram of the gas-liquid separator and oil-waterseparator of the FIG. 1 embodiment;

FIG. 3 is a schematic representation of an alternate embodiment of thepresent invention in which production fluid is delivered to thegas-liquid separator by way of an annular space located within thewellbore;

FIG. 4 is a schematic diagram of the gas-liquid separator and oil-waterseparator of the FIG. 3 embodiment; and

FIGS. 5a to 5 d are more detailed schematic representations of types ofgas-liquid separators illustrated in FIGS. 1 to 4: FIG. 5a illustrates agas-liquid separator that includes a cyclone with a combined swirlintake/gas outlet; FIG. 5b illustrates a gas-liquid separator thatincludes a cyclone with swirl intake and a gas segregation finder; FIG.5c illustrates a gas-liquid separator that includes a cyclone with acombined swirl intake/gas outlet and an auger; and FIG. 5d illustrates agas-liquid separator that includes a cyclone with a combined swirlintake/gas outlet and an auger, with the auger gas outlet extending intothe combined swirl intake/gas outlet.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The description which follows, and the embodiments described therein,are provided by way of illustration of an example, or examples ofparticular embodiments of the principles of the present invention. Theseexamples are provided for the purpose of explanation, and notlimitation, of those principles and of the invention. The examplesinclude a description of the best mode of practising the inventioncurrently known to the inventors.

With reference to FIG. 1 and FIG. 3, there is shown hydrocarbonproduction well 10 having wellbore casing 12 that penetrates at leastone production formation 14 and at least one injection formation 16.Production perforations 18 in the wellbore casing are provided in thearea of the production formation 14 to allow for inflow of the producedmixture from production formation 14. Injection perforations 20 in thewellbore casing are provided in the area of injection formation 16 toallow for injection of water into injection formation 16. Injectionformation 16 may be above or below production formation 14. Lowerannular sealing packer 22 isolates production formation 14 frominjection formation 16. Separator 24, to separate water, gas andhydrocarbon contained in the produced mixture, is located withinwellbore casing 12 above production formation 14. In FIGS. 1 through 4,separator 24 has been illustrated as a simple schematic and one skilledin the art can appreciate that the separator is more complicated. Also,in FIG. 1 and FIG. 3, separator 24 is located near the head of the well.In other embodiments, its location may be lower in the well. In otherembodiments, its location may be higher in the well.

In FIG. 1, total production conduit 26 extends within wellbore casing 12from production formation 14 to separator 24 for flow of the totalproduced mixture in the direction indicated by arrow 28. In thisembodiment, gas-lift is provided through one or more gas-lift valves 30spaced along the length of total production conduit 26 that extends intothe wellbore to aid in lifting the produced mixture up the well.Alternative embodiments of the gas lift system will be apparent to thoseskilled in the art. For example, a continuous gas lift system may beused. An intermittent gas lift system may also be used. In wells wherethe eruptive force of the well is sufficient to lift the produced fluidsup the well naturally, gas-lift may not be required. Upper annularsealing packer 32 isolates the production formation from annular space34 in the well. Means for introducing lift gas (not shown), flowing inthe direction indicated by arrows 36, is provided for on the surface.Separator 24 includes, in this embodiment, gas-liquid separator 38 andoil-water separator 40. Gas-liquid separator 38 reduces the fraction offree gas in the produced mixture entering oil-water separator 40. Theproduced mixture from the production formation can contain gas, oil andlarge amounts of water in the oil, as well as other impurities. In apreferred embodiment, there is a high water cut, for example 80% watercut, in the produced fluids. In other preferred embodiments, the watercut is higher or lower. This mixture flows from production formation 14to separator 24, shown in FIG. 2, through total production conduit 26and enters the upper portion of gas-liquid separator 38, throughproduction fluid inlet 42. Accordingly, gas is separated from the totalproduced mixture by gas-liquid separators of the types shownschematically in FIGS. 5a to 5 d, and free gas, travelling in thedirection indicated by arrow 44, exits gas-liquid separator 38 throughupper port 46 of gas collection conduit 48. Alternative embodiments ofthe gas-liquid separators illustrated in FIGS. 5a to 5 d will beapparent to one skilled in the art. The gas-depleted produced mixture,travelling in the direction indicated by arrow 50, exits gas-liquidseparator 38 through liquid outlet 52 and enters oil-water separator 40.Oil-water separator 40 includes separation chamber 56 wherein gasdepleted production fluid is separated into a predominately hydrocarboncomponent and a predominately water component using cyclone separator58. Alternative embodiments of the oil-water separator to separate theproduced mixture into a predominately hydrocarbon component and apredominately water component will be apparent to one skilled in theart. For example, one or more cyclones can be housed in one or moreseparators, which, in turn, can act in series or in parallel, toseparate produced fluids. The predominately hydrocarbon component,travelling in the direction indicated by arrow 60, exits separationchamber 56 and travels through oil concentrate conduits 62 which extendup the wellbore to conduit 66, which, in turn, extends to the head ofthe well. Gas collection string 48 is connected in this embodiment toconduit 62 through junction 68, so that free gas travelling in thedirection indicated by arrow 44 and hydrocarbon travelling in thedirection indicated by arrow 67 are lifted to the wellhead commingled.In another embodiment, a pressure drop device such as an orifice can beutilized to commingle the predominately hydrocarbon component and gas.The predominately water component, travelling in the direction indicatedby arrow 70, exits oil-water separator 40 into water disposal string 74.Water disposal string 74, preferably equipped with adjustable downholechoke 76, passes through lower annular sealing packer 22 and extendsfrom the bottom of separator 24 to injection formation 16. Thepredominately water component flows in the direction indicated by arrow78, to injection formation 16.

In FIG. 3, another embodiment of this invention is disclosed. Elementspreviously described have been given the same reference number. Thetotal produced mixture flows in the direction indicated by arrow 28, upthe wellbore to separator 24 through annular space 34 located in thewellbore. In this embodiment, annular space 34 is formed between thecasing of the well and water disposal string 74. Using an annular spacefor the flow of the produced mixture can allow for larger flow area andhigher capacity that using a dedicated tubing for flow of the producedmixtures. Gas-lift string 80 traverses down the wellbore casing 12 fromthe head of the well to the lowest desired gas injection point. In thisembodiment, the desired location is above the production formation. Ingeneral, the gas-lift string extends to a location below the wellheadbut above the production formation. To assist in lifting totalproduction fluid to separator 24, gas, flowing in the directionindicated by arrow 36, is provided through gas-lift string 80 having oneor more gas-lift valves 30 spaced along the length of gas-lift string80. Production fluid enters the upper portion of gas-liquid separator38, shown in detail in FIG. 4, through one or more inlets 82.Accordingly, gas is separated from the total produced mixture bygas-liquid separators of the types shown schematically in FIG. 5. Freegas, flowing in the direction indicated by arrow 44, exits gas-liquidseparator 38 through upper port 46 of gas collection string 48. Thegas-depleted produced mixture, flowing in the direction indicated byarrow 50, exits gas-liquid separator 38 through liquid outlet 52 andenters oil-water separator 40 shown in FIG. 4. Oil-water separator 40includes separation chamber 56 wherein the gas depleted produced mixtureis separated into a predominately hydrocarbon component and apredominately water component using cyclone separator 58. Alternativeembodiments of the oil-water separator to separate the produced mixtureinto a predominately hydrocarbon component and a predominately watercomponent will be apparent to one skilled in the art. For example, oneor more cyclones can be housed in one or more separators, which, inturn, can act in series or in parallel, to separate produced fluids. Thepredominately hydrocarbon component, flowing in the direction indicatedby arrow 60, exits separation chamber 56 through oil concentrateconduits 62 which in turn extend up the wellbore to conduit 66, thatextends to the surface. The predominately water component, flowing inthe direction indicated by arrow 70, exits oil-water separator 40 intowater disposal string 74. Water disposal string 74, preferably equippedwith adjustable downhole choke 76, passes through lower annular sealingpacker 22 and extends from the bottom of separator 24 to injectionformation 16. Water flows in the direction indicated by arrow 78 toinjection formation 16.

Referring now to FIGS. 5a to 5 d, schematics of various types of thegas-liquid separator component of the present invention are shown. FIG.5a shows the gas-liquid separator of the present invention whichincludes a cylindrical cyclone 83 with a combined swirl intake/gasoutlet 84 and vortex breaker 91. FIG. 5b shows the gas-liquid separatorof the present invention, which includes a cylindrical cyclone 83 withswirl intake 84, gas segregation finder 86 and vortex breaker 91. FIG.5c shows the gas-liquid separator of the present invention, whichincludes cylindrical cyclone 83 and combined swirl intake/gas outlet 89and auger 88. FIG. 5d shows the gas-liquid separator of the presentinvention which includes cyclone 83 with combined swirl intake/gasoutlet 90, and auger 88, with the auger gas outlet extending into thecombined swirl intake/gas outlet 90.

While the invention has been described with reference to certainembodiments, it is to be understood that the description is made only byway of example and that the invention is not to be limited to theparticular embodiments described herein and that variations andmodifications may be implemented without departing from the scope of theinvention as defined in the claims hereinafter set out.

What is claimed is:
 1. A method for the downhole separation andinjection of a predominately water component of a production fluidcomprising at least some oil and at least some water from a productionformation of a hydrocarbon well, the method comprising the steps of: (a)separating downhole, at a position elevated with respect to a downholeinjection formation, the production fluid into a predominately watercomponent and a predominately hydrocarbon component; and (b) deliveringthe predominately water component to the downhole injection formation,wherein; (c) the separating step is conducted at a sufficiently elevatedlocation with respect to the injection formation to permit thepredominately water component of step (b) to be delivered to thedownhole injection formation under the force of gravity; whereindelivery of the production fluid to the elevated position is promoted byinjecting gas into the fluid.
 2. The method as recited in claim 1,wherein the percentage of water in the production fluid is at least 20%.3. The method as recited in claim 1, wherein the production fluidcontains gas, further comprising the step of: (d) separating gas fromthe production fluid, and wherein: optionally, step (d) precedes step(a), and/or further comprising the step of delivering gas separated fromthe production fluid to the surface.
 4. The method as recited in claim1, further comprising the step of transporting the mostly hydrocarboncomponent to the surface.
 5. The method as recited in claim 4, whereingas lift is used to transport the mostly hydrocarbon component to thesurface.
 6. The method as recited in claim 3, further comprising thesteps of: (e) combining gas produced in step (d) and the predominatelyhydrocarbon component produced in step (a); and (f) delivering thecombined mixture obtained in step (e) to the surface.
 7. The method asrecited in claim 6, wherein a mixing device is used to combine gasproduced in step (d) and the predominately hydrocarbon componentproduced in step (a).
 8. The method as recited in claim 1, wherein theproduction fluid is delivered to the elevated position of step (a) byway of a conduit extending from the production formation to the elevatedposition.
 9. The method as recited in claim 1, wherein there is anannular space in the well, and the production fluid is delivered to theelevated position of step (a) through the annular space.
 10. The methodas recited in claim 1 wherein the injected gas is delivered downholethrough a gas-lift string extending from the head of the well to asuitable downhole location.
 11. A method for the downhole separation andinjection of a predominately water component of a production fluidcomprising at least some oil and at least some water from a productionformation of a hydrocarbon well, the method comprising the steps of: (a)injecting gas into the production fluid so as to lift the productionfluid to a position in the wellbore that is elevated with respect to aninjection formation; (b) separating downhole, at the elevated position,gas from the production fluid; (c) separating downhole, at the elevatedposition, the production fluid into a predominately water component anda predominately hydrocarbon component; (d) delivering the predominatelywater component to the downhole injection formation, wherein; (e) theseparating steps are conducted at a sufficiently elevated location withrespect to the injection formation to permit the predominately watercomponent of step (c) to be delivered to the downhole injectionformation under the force of gravity; (f) transporting gas separatedfrom the production fluid to the surface; and (g) transporting themostly hydrocarbon component of the production fluid to the surface. 12.A system for the downhole separation and injection of a predominatelywater component of a production fluid comprising at least some oil andat least some water from a production formation of a hydrocarbon well,the system comprising: (a) an oil-water separator located downhole at aposition elevated with respect to an injection formation; (b) a firstpassage extending between the production formation and an inlet of theseparator to provide fluid communication therebetween; and (c) a secondpassage, isolated from the first passage, extending between a wateroutlet of the separator and the downhole injection formation to providefluid communication therebetween; wherein: (d) the separator is locatedat a sufficiently elevated location with respect to the injectionformation to permit fluid emerging from the water outlet to be deliveredto the downhole injection formation under the force of gravity; and (e)means for injecting gas into the production fluid for delivery thereofto the separator.
 13. The system as recited in claim 12, furthercomprising a gas-liquid separator located at an elevation at least ashigh as the oil-water separator and located inline for receivingproduction fluid, the gas-liquid separator having a gas-liquid inlet influid communication with the first passage, for receiving productionfluid therethrough, and a liquid outlet in fluid communication with thefirst passage, to permit flow of liquid from the gas-liquid separator tothe oil-water separator.
 14. The system as recited in claim 12 or 13,further comprising a third passage extending between an oil outlet ofthe oil-water separator and a head of the well.
 15. The system asrecited in claim 14, further comprising means for injecting gas into thethird passage to promote flow of fluid from the oil outlet of theoil-water separator to the head of the well.
 16. The system as recitedin claim 15, wherein the means for injecting gas into the third passagecomprises a conduit providing fluid communication between a gas outletof the gas-liquid separator and the third passage.
 17. The system asrecited in claim 12, wherein the oil-water separator comprises at leastone cyclone.
 18. The system as recited in claim 13, wherein theoil-water separator comprises at least one cyclone.
 19. The system asrecited in claim 12, wherein the means for injecting gas into theproduction fluid comprises a conduit extending between a head of thewell and a suitable location downhole.
 20. The system as recited inclaim 13, wherein the gas-liquid separator comprises a cyclone.
 21. Thesystem as recited in claim 13, wherein the gas-liquid separatorcomprises an auger.
 22. A method of completing a well for the downholeseparation and injection of a predominately water component of aproduction comprising at least some oil and at least some water fluidfrom a production formation of a hydrocarbon well, the methodcomprising: (a) installing an oil-water separator downhole at a positionelevated with respect to an injection formation; (b) providing a firstpassage extending between the production formation and an inlet of theseparator to provide fluid communication therebetween; and (c) providinga second passage, isolated from the first passage, extending between awater outlet of the separator and the injection formation of the well toprovide fluid communication therebetween; wherein: (d) the separator islocated at a sufficiently elevated location with respect to theinjection formation to permit fluid emerging from the water outlet to bedelivered to the downhole injection formation under the force ofgravity; and (e) means for injecting gas into the production fluid fordelivery thereof to the oil separator.
 23. The method as recited inclaim 22, further providing a gas-liquid separator located at anelevation at least as high as the oil-water separator and located inlinefor receiving production fluid from the production formation, thegas-liquid separator having a gas-liquid inlet in fluid communicationwith the first passage, for receiving production fluid therethrough, anda liquid outlet in fluid communication with the first passage, to permitflow of liquid from the gas-liquid separator to the oil-water separator.24. The method as recited in claim 22, further providing a third passageextending between an oil outlet of the oil-water separator and a head ofthe well.
 25. The method as recited in claim 24, further providing meansfor injecting gas into the third passage to promote flow of fluid fromthe oil outlet of the oil-water separator to the head of the well. 26.The method as recited in claim 25, wherein providing the means forinjecting gas into the third passage comprises installing a conduit forfluid communication between a gas outlet of the gas-liquid separator andthe third passage.
 27. The method as recited in claim 22, whereinproviding the oil-water separator comprises installing at least onecyclone.
 28. The method as recited in claim 22, wherein providing themeans for injecting gas into the production fluid comprises installing aconduit which extends between a head of the well and a suitable locationdownhole.
 29. The method as recited in claim 23, wherein providing thegas-liquid separator comprises installing a cyclone.
 30. The method asrecited in claim 23, wherein providing the gas-liquid separatorcomprises installing an auger.